1. Field of the Invention
The present invention relates to a method of image transformation for enlarging, reducing or rotating a digital image for display in an image display device which is used for processing and displaying the digital image, such as a display device or a printer.
2. Description of the Prior Art
In a display device or a printer which displays characters, symbols, line segments or graphic patterns, it is often necessary to output characters and symbols in a variety of sizes for various reasons, such as for the purpose of calling the attention of a user to certain information or putting headings or footnotes in the display.
In such a case, it may be possible to produce patterns such as characters and symbols of different respective sizes, but this raises the problem that an increase of memory capacity is required for storing the increased number of patterns of different sizes. If patterns of any desired size can be generated from patterns of a single size, such as character patterns or symbol patterns, the memory capacity can be maintained. The advantage of the above is remarkable particularly when several thousands of KANJI character patterns are to be displayed.
It has been proposed to represent each picture element of a digital pattern as shown in (a) of FIG. 1 by n.times.m picture elements in a pattern as shown in (b) of FIG. 1 (in which n=m=3) or to make an interpolation when diagonal black picture elements are present in order to compensate for jaggyness of the diagonal line when the digital pattern is displayed by the above method, as disclosed in the Japanese Published Unexamined Patent Application No. 50-10925. However, those approaches are not practical because the pattern can be enlarged only by a factor of an integer.
In the Japanese Published Unexamined Patent Application 50-3732, it is proposed to detect transitional points from white to black picture elements or black to white picture elements in rows and columns, determine projection distributions of the transitional points in rows and columns, compare the projection distributions in rows and columns, rearrange the projection distributions in the order of their magnitude and select information of only a desired number of rows and columns depending on a desired reduction factor so that any desired non-integer reduction factor may be attained.
In this method, however, it is necessary to detect the transitional points in rows and columns, determine the projection distributions in rows and columns, rearrange the projection distributions in the order of magnitude and select the desired row and column information in order to obtain the desired pattern. Thus, if those steps are to be implemented by hardware, large scale hardware equipment is required. If they are to be implemented by a software technique, a long process time is required.